All posts in category Fish

Recently, the blackspot tuskfish (Choerodon schoenleinii) became a media sensation when it was captured in photos using a rock as tool to open a clam. Apparently not happy with the print media attention afforded to its relative, the orange-dotted tuskfish (Choerodon anchoago) has taken the behavior to the movies, digging up a clam with its pectoral fin, swimming about five meters with it, and then crushing it open using a rock as an anvil:

…

As reported in the latest issue of Coral Reefs, a diver off the coast of Palau observed the orange-dotted tuskfish using a rock as a tool on three separate occasions, capturing the above footage on the final instance. The paper notes that three separate genera of wrasses (the Choerodon that have been in the news lately, as well as the Halichoeres and Thalassoma) have now been seen using similar sideways head movements to slam bivalves against rock anvils, suggesting that this may be a “deep-seated behavioral trait” in wrasses and, potentially, other groups of fishes.

The archerfish is a small fish that earns a living by shooting prey – insects, spiders and even small lizards – out of the sky, knocking them off twigs and leaves and into the water with an incredibly accurate jet of water launched from its mouth. Here’s a brief video that shows off the archerfish’s hunting skills:

…

Pretty incredible, huh?

Complex Calculations

And this brings us to the topic of the archerfish’s specialized and complex cognitive abilities.

As the video notes, because the archerfish hunts from beneath the water’s surface, it must be able to take into account both the bending of light at the surface of the water and the curvature of the water stream it shoots toward a target perched as much as two meters away. I’m not aware of any studies on how adept humans are at shooting water pistols at above-ground targets while snorkeling, but in an accuracy contest, I’m betting on the archerfish.

Additionally, in a report published in Current Biology1 in 2006, researchers from Erlangen-Nürnberg University in Germany showed that the archerfish not only aim accurately, but are able to save energy by estimating the size of their prey and modifying the amount of water they shoot. Using high speed photography, the researchers “discovered that archerfish transfer systematically larger maximum forces to larger targets … for any given size of prey, the fish apply about ten times the forces the adhesive organs of prey of that size could maximally sustain.”

Dinner is served! (photo credit: Peter Arnold)

In a later study published in Science2, the same research group elaborated on the efficiency and speed with which archerfish are able to swim to the precise spot where their prey will land after being hit by a water jet. (Because archerfish hunt in groups and are surrounded by other surface-feeders, they have to be able to swim to fallen prey extremely quickly or they will lose it to another hungry mouth.)

The researchers found that archerfish are able react to the motion of falling prey and start swimming to the correct spot at the correct speed within as little as 40 milliseconds, 1/20 of a second. Moreover, the archerfish accomplish this complex task (which requires them to process a host of variables, including the initial height of the prey, the speed of the fall, and the direction in which it is falling) using relatively few neurons and without reference to a priori information regarding the trajectory of the water jet that hit the prey. As the researchers summarized it, “our data show that even complex decisions can be made rapidly and accurately by a relatively small number of neurons.”

So, as we consider the meaning of the archerfish’s impressive skills, we should bear in mind that sophisticated cognitive behavior can evolve to address the particular tasks and challenges facing a species, and that even an animal with a small, non-mammalian brain can accomplish “super-human” cognitive feats if those feats help the animal to successfully adapt to its ecological niche.

Tool Use?

One final question is whether the archerfish is engaging in tool use when it shoots down its dinner with jets of water. We touched on this in the earlier post regarding the fearsome clam-smashing tuskfish, noting Jane Goodall’s definition of tool use as “the use of an external object as a functional extension of mouth or hand in the attainment of an immediate goal.” While there will undoubtedly continue to be debate and disagreement over the definition of tool use, some points to ponder for now include:

Does the water used by the archerfish constitute an “external object” within the meaning of the Goodall definition? On the one hand, the water was external to the archerfish until it decided to use it to shoot down prey; on the other, the water obviously is not external right at the moment it is launched.

Does the “external object” need to be solid, as alluded to in the earlier tuskfish post? Why should the consistency of the object matter?

Can one argue that the archerfish is transforming the nature of the water (from a surrounding environmental medium into a targeted projectile)? If yes, does this imply that the archerfish’s use is more sophisticated than, say, simply picking up a rock lying outside on the ground (or a monkey wrench hanging on an Ace Hardware rack) and using it as is?

Some researchers have described behavior that meets some, but not all, of the requirements of a strict tool use definition as “proto” or “borderline” tool use. Is that what we are talking about here?

Should the behavior speak for itself without attempting to attach a label to it? Why does it matter whether or not we categorize the behavior as tool use? Is there something anthropomorphic about the “tool use” label in the first place?

These are all interesting questions, at least for those of us who are not preoccupied with shooting our dinner out of the sky.

As reported last week in ScienceNOW1, a professional diver exploring the Great Barrier Reef off the coast of Australia recently snapped the first photos of a fish using tools. The diver, Scott Gardner, came across a blackspot tuskfish (Choerodon schoenleinii) that was hovering over a sandy area near a rock with a clam in its mouth. The tuskfish rolled on its side and, with a repeated cracking noise, slammed the clam against the rock until the shell fractured. Here’s one of the photos that Gardner took of the industrious (and hungry) tuskfish:

Tuskfish cracking open clam (photo credit: Scott Gardner)

While there have been anecdotal accounts of other fish using tools, this is the first time that this type of behavior has been caught on film.

What Is Tool Use, Anyhow?

In an interesting aside, this incident has brought to the forefront some of the ways in which it is difficult to define, and reach agreement upon, exactly what constitutes “tool use” in animals. As noted in the ScienceNOW article, there has been previous debate over whether stingrays and archerfish targeting jets of water to capture prey constitutes tool use (is a solid external object necessary for there to be a tool?), as well as whether tool use “requires the animal to hold or carry the tool itself, in this case the rock.”

The research paper regarding this tuskfish behavior, which was published in the most recent issue of Coral Reefs2, the official Journal of the International Society for Reef Studies, argues that the tuskfish using the rock as an anvil to open the clam conforms to a definition of tool use first formulated by Jane Goodall back in 1970, that tool use is “the use of an external object as a functional extension of mouth or hand in the attainment of an immediate goal.” The paper adds: “The use of a rock as an anvil rather than a hammer could be considered a sign of intelligence considering the ineffectiveness of manipulating a freely suspended tool in water. The images certainly provide an interesting starting point for further comparative studies on tool use in fishes.”

The ScienceNOW article describes how Culum Brown, a behavioral ecologist at Macquarie University in Sydney, Australia, and a co-author of the Coral Reefs paper:

argues that it’s not logical to apply the same rules to fish as to primates or birds. For one thing, fish don’t have anything but their mouths to manipulate tools with, and for another, water poses different physical limitations than air. ‘One of the problems with the definition of tool use as it currently stands is it’s totally written for primates,’ he says. ‘You cannot swing a hammer effectively underwater.’

Those of you who pay close attention may already have noted that the definition of tool use can stir controversy. For example, beginning at the 10:34 mark in her video presentation relating to the awesome octopus, Maggie Koerth-Baker describes two very divergent definitions that might lead to different conclusions about whether the octopus engages in tool use: (a) a stricter definition that requires that an animal use a solid object to solve an “immediate problem,” rather than just to provide defense, and (b) a broader definition holding that tool use occurs whenever an animal modifies an object so as to alter some aspect of its environment.

Food For Thought

In considering tool use by animals, here are some things you might want to ponder:

Which of the above definitions makes the most sense to you?

Does it matter whether the behavior is performed by a captive animal (like the New Caledonian crow) or in the wild?

Are definitions of tool use inherently anthropocentric and subjective? That is, are we trying to come up with a definition that basically requires the behavior to look like something a human would do (if it really is a tool, then I should be able to see the Craftsman logo) before we accept it?

Is it significant whether the behavior is widespread? That is, if the behavior is only observed once or twice, is it a fluke? If the behavior is widespread, is it mere instinct?

Is nest building by birds an example of tool use?

Conclusion

There will undoubtedly be more AnimalWise posts about tool use. In the meantime, if you run across any tuskfish, you should look very closely to see if you can see their very small, teeny-tiny tool belts. They really are quite cute.

Here are some more photos (note, the following pictures may not be suitable for small children and clams):

We are all familiar with talented sports teams that underachieve because, despite the individual abilities of their players, they’ve been unable to “pull together” and coordinate their efforts effectively. Because teamwork requires cooperation, communication, and complex social interaction, we typically bring in outside coaches to create an environment that allows teamwork to develop, and we reserve our highest praise (and compensation) for those rare players who have the gift of making others better while being successful themselves (just ask Magic Johnson and Larry Bird).

With that in mind, you may be surprised to learn that a couple of the world’s most accomplished team players can be found not on the playing field or in the arena, but under the sea, and that they are members of different species of fish.

Grouper (from Wikipedia; photo credit: Jon Hanson)

In recent research published in PLoS Biology1, scientists reported on a highly coordinated and communicative hunting partnership between the grouper and the giant moray eel, which they observed in the coral reefs of the Red Sea. Together, the two fish make an extremely complementary and formidable hunting team.

Groupers, large predatory reef fish, are daytime hunters, while morays usually hunt at nght and rest in crevices during the day. Groupers typically hunt in open water near reefs and have trouble catching fish that hide in the holes and crevices that they find in the coral. Moray eels, on the other hand, sneak around reef crevices and attempt corner prey in holes, but have trouble catching fish in open water.

Giant Moray Eel (from Wikipedia; photo credit: Albert Kok)

As the research report observed: “The hunting strategies of the two predators are therefore complementary, and a coordinated hunt between individuals of the two species confronts prey with a multipredator attack that is difficult to avoid; prey are not safe in open water because of the grouper hunting strategy but cannot hide in crevices because of the moray’s mode of attack.”

The researchers found that hungry groupers would actively seek out their moray eel fishing partners in their crevices and shake their heads rapidly right in the eels’ faces to let them know that it was time to go for a hunt. Here’s a video of a grouper letting an eel know that it is time to eat.

The morays would then leave their hiding holes and swim off in search of food with the groupers. Here’s a video of the hunting twosome happily swimming off together for dinner.

Moreover, the pair would cooperate as they hunted. In some cases, for instance, a grouper would remain directly above a crevice where prey was hiding, perform “headstands” and shake its head to guide the moray eel to the hidden prey’s location.

The researchers noted that, when the two fish worked together as a team, the groupers caught five times as many fish as they did separately, and the moray eels caught almost twice as many fish as the groupers. (Because the morays normally hunt at night, the researchers didn’t observe them catching any fish separately, so they were not able to draw any conclusions regarding how their partnership with the groupers changed their hunting efficiency.)

This type of inter-species coordinated hunting with differentiated roles is extremely rare and had never been seen before in fish. If you think about it, this is pretty complex and advanced behavior, as the individuals must perform specific actions and play specific roles, knowing that their counterparts are doing the same. The groupers, with their intentional signaling to call their moray partners to the hunt and to direct them to prey, demonstrate particularly sophisticated, cognitively advanced behavior.

So, forget about your local sports franchise; if you want to see some especially impressive teamwork, you should put on your wetsuit and let some reef fish show you how it’s done.

Do not fear mistakes. You will know failure. Continue to reach out.Benjamin Franklin

Nice quotes, but I think I’ll just avoid making mistakes, thank you very much.Stickleback Fish

When you or I make a mistake, we can seek comfort in witty sayings, self-help programs and expensive therapy sessions. When a nine-spined stickleback fish makes a mistake, it often ends up in the belly of another marine animal.

Nine-Spined Stickleback (BBC News)

Perhaps motivated by this rather unpleasant truth, sticklebacks – a small fish commonly found in North America, Europe and Asia – have developed some unusually sophisticated social learning capabilities. In particular, sticklebacks are able to compare the feeding behavior of other sticklebacks with their own experience and choose which fish to copy in order to find more food. This capability, sometimes referred to as a “hill climbing” strategy, has not been observed in any animals other than sticklebacks and humans … at least those humans who aren’t too busy making mistakes in order to enjoy character-building learning opportunities. More importantly (to the sticklebacks), this voyeuristic approach to feeding enables them to learn where to feed while relaxing in safe places rather than running a gauntlet of predators to search for feeding sites in the open.

In a study published in Behavioral Ecology1, English researchers placed 270 sticklebacks in a tank with two feeders, one of which – the “rich feeder” – supplied a lot more food than the other. The fish that learned to prefer the rich feeder were then allowed to watch other sticklebacks feeding in the same tank but, this time, the rich feeder no longer provided more food (in some cases, it provided less food, in others it provided about the same amount of food). When the observing group was given another opportunity to feed, about 75% were “clever” enough to know from watching the other fish that they should avoid the formerly rich feeder if it was now giving out less food, choosing the new improved feeder instead. However, in situations where the change in feeders resulted in each providing roughly the same amount of food, the observers did not copy the other fish and stuck with their initial choice.

As reported in ScienceDaily2, the BBC News3, and the Guardian4, one of the authors, professor Kevin Laland from the School of Biology at St Andrews University, saluted the sticklebacks for their learning prowess: “Nine-spined sticklebacks may be the geniuses of the fish world. It’s remarkable that a form of learning found to be optimal in humans is exactly what these fish do.” Another researcher, Jeremy Kendal from Durham University’s anthropology department added: “Hill-climbing strategies are widely seen in human society whereby advances in technology are down to people choosing the best technique through social learning and improving on it, resulting in cumulative culture. But our results suggest brain size isn’t everything when it comes to the capacity for social learning.”

So, in a fish eat fish world where mistakes can be costly, we would be well advised to balance our trial by error tendencies against the wisdom of a species that has learned how to succeed without putting itself into jeopardy.